Assalamualaikum. In the past, I didn't know tajweed and could not recite the Qur'an correctly. So, I used to make big mistakes in surahs in my prayers. Should I redo all my prayers again?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

You do not have to repeat any prayers if you make pronunciation mistakes in the recitation after Al-Fatihah whether these mistakes change the meaning or not as long as it is not intentional. The recitation after Al-Fatihah is originally Sunnah, and the prayer is not invalid by reciting with mistakes or by not reciting (at all). So long as you were reciting Al-Fatihah correctly, your last prayers are valid and sufficient. Furthermore, if it was assumed that you were making a mistake in Al-Fatihah out of ignorance and you recited it while making mistakes that change the meaning, then some scholars are of the view that whoever ignorantly leaves one of the conditions of prayer does not have to repeat it. This is the view chosen by Shaykh al-Islam Ibn Taymiyyah and you can act upon this view in order to ward off embarrassment and relieve hardship.

Allah knows best.